Sheet for Providing a Barrier

ABSTRACT

A sheet for providing a barrier against the penetration of insects, the sheet comprising at least one insecticide distributed through a plastics material wherein the insecticide is substantially retained in the plastics material.

FIELD OF THE INVENTION

The present invention relates to sheets for providing a barrier againstthe penetration of insects and methods of protecting a building againstthe penetration of insects into the building.

BACKGROUND TO THE INVENTION

Buildings may be subject to entry by insects. Some insects, such astermites will damage the building. In general, termites enter thebuilding where it contacts the ground. From there, the termites mayspread rapidly throughout the building, causing significant damage toany timber.

As a result, physical barriers have been employed to guard against theentry of insects, particularly termites to buildings. Typically, thesebarriers are in the form of plastic sheets and are placed either under aconcrete slab or the entire building including the footings (ie. in fullsoil contact), whereby the plastic sheet also acts as a moisturebarrier. The main problem with using plastic sheeting is that sometermites are capable of eating through the plastic, thereby causing abreakdown of the physical barrier to their entry into the building.

To overcome this problem, a number of approaches have been proposed inwhich use of the plastic sheet is combined with the use of aninsecticide. In one approach, the plastic sheet incorporates aninsecticide either throughout the sheet or in localised areas of theplastic sheet, whereby the insecticide is controllably released orleached from the plastic into the surrounding soil. A “buffer zone”around the plastic sheet is thus created, in which insects will bekilled should they enter this zone. One of the most significant problemswith this approach is that once the insecticide has substantiallyleached from the plastic, then the sheet becomes nothing more than theplain plastic sheet, with its associated problems, discussed above.Thus, the plastic sheet which leaches an insecticide has an effectivelifetime which is limited by the leaching rate of the insecticide.Another problem with the insecticide leaching plastic sheet is that therelease of such chemicals into the general environment may harm theenvironment and kill other organisms. Furthermore, the insecticide maybe washed from the soil during heavy rain fall, which may result inpollution to run-off as well as the loss of the lethal “buffer zone”.Furthermore, the insecticide leaching plastic sheet has only limitedapplications because, in order to work, it requires a substrate intowhich the termiticide can leach.

In an alternative, a liquid insecticide, typically deltamethrin iscontained between two sheets of impermeable plastic. Thus, when theplastic is chewed through by termites, the liquid insecticide isreleased into a localised area around the penetration point where itkills any termites which are present. However, there are severalproblems with this arrangement as well, one of these being that once theplastic has been breached and the insecticide released, that there is nofurther termiticide barrier. Of further concern with this approach isthat release of concentrated insecticide (ie. in liquid form) may causeharm to the local environment. Concentrated insecticides also pose asubstantial health risk to humans. Thus, this type of barrier could notbe used in a location where it would be likely that humans would come incontact with the liquid insecticide, such as at or above ground level.Another problem, is that the plastic/liquid insecticide sheeting isdifficult and dangerous to handle because it is bulky and also becausewhen it is cut to shape for use, the person handling the sheeting isoften exposed to the liquid insecticide.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention, there is provideda sheet for providing a barrier against the penetration of insects, thesheet comprising at least one insecticide distributed through a plasticsmaterial wherein the insecticide is substantially retained in theplastics material.

Because the insecticide is retained, the insecticide does notsubstantially leach from the plastics material. Thus, its activity isexpressed throughout the plastics material.

In use, the plastics material provides a physical barrier against thepenetration of insects and the insecticide provides a chemical barrieragainst the penetration of insects.

Preferably, the surfaces of the sheet are substantially identical,whereby, in use, the sheet may be laid with either surface facing up.

Preferably, the sheet is approximately 0.1-1 mm thick.

Preferably, the sheet is approximately 0.2-0.5 mm thick.

Preferably, the sheet is approximately 0.2 or 0.5 mm thick.

Preferably, the plastics material is any synthetic or semi-syntheticcompound formed by organic condensational polymerisation.

Preferably, the plastics material is any plastics material which can bemoulded or extruded into objects or films or fibres.

Preferably, the plastics material is any one or a combination ofpolyamide (nylon), polyethylene, ethylene vinyl acetate, polystyrene,polyvinylchloride, synthetic rubber (eg. neoprene),polymethylmethacrylate (acrylic), polypropylene and polyurethane.

Preferably, the plastics material is low density polyethylene.

Preferably, the plastics material contains a UV stabiliser.

Preferably, the plastics material contains a white colouring agent.

Preferably, the sheet is substantially impact resistant according toAustralian standard AS 4347.6.

Preferably, the sheet is substantially impermeable to water.

Preferably, vapour permeance through the sheet is less than 0.02 mg/Ns.

Preferably, the at least one insecticide is any compound that exhibitssufficient lethal control and/or repellent effects against insects.

Alternatively, a separate repellent compound in addition to theinsecticide is distributed through the plastics material.

Preferably, the repellent compound does not significantly leach from theplastics material.

In use, the repellent compound provides a repellent barrier against thepenetration of insects in addition to the chemical and physical barrier.

Preferably, the at least one insecticide is any one or combination ofpyrethrum, synthetic pyrethroids, organo-chlorines, organo-sulfurs,carbamates, organo-phosphates, formamidines, nicotinoids, spinosyns,phenylpyrazoles, pyrroles, pyrazoles, dinitrophenols, pyridazinones,quinazolines, and benzoylureas.

Typically, the insects impeded by the sheet will be termites.

Preferably, the at least one insecticide is a termiticide.

Preferably, the termiticide is a synthetic pyrethroid.

Preferably, the termiticide is any one or combination of bifenthrin,permethrin, deltamethrin, lambda-cyhalothrin, cypermethrin,alpha-cypermethrin, tetramethrin, and cyfluthrin or any other syntheticpyrethroid.

Preferably, the concentration of insecticide in the plastic is less than5 weight %.

Preferably, the concentration of insecticide in the plastic is greaterthan 0.01 weight %.

Preferably, the insecticide is bifenthrin.

Where the insecticide is bifenthrin, its concentration in the plastic ispreferably 0.05 to 1.0 weight %.

Preferably, the bifenthrin has a concentration of approximately 0.05-0.1weight %, more preferably, approximately 0.1 weight %.

Bifenthrin provides a repellent barrier as well as a chemical barrier tothe penetration of termites.

Preferably, the sheet is formed in a blown film extrusion process.Alternatively, the sheet is formed in an extrusion process. Preferably,the sheet is formed in the extrusion process if it has a thickness ofapproximately 0.5 mm. If the sheet has a thickness of approximately 0.2mm, then preferably it is formed in the blown film extrusion process.

Preferably, the sheet is formed from a master batch of plasticcontaining insecticides.

Preferably, the master batch has a concentration of insecticide which isstably supported in the plastic.

Preferably, at least one surface of the sheet is embossed.Alternatively, at least one surface of the sheet is smooth.

According to a second aspect of the present invention, there is provideda method of protecting a building against the penetration of insectsinto the building, the method comprising the step of positioning one ormore sheets of a plastics material above the footings of the building,wherein the plastics material contains at least one insecticidedistributed therethrough.

Preferably, the step of positioning the sheets of plastics materialfurther involves positioning the sheets around the perimeter of thebuilding at least extending between an outer wall of the building and aninner frame of the building.

In this arrangement, the sheets of plastics material restrictpenetration by insects to the perimeter cavity between the outer walland inner frame.

Preferably, the step of positioning the sheets of plastics materialfurther involves positioning the sheets under all or part of a concreteslab of the building.

Preferably, the insecticide is substantially retained in the plasticsmaterial.

Preferably, the sheet acts as a moisture barrier for at least a portionof the building.

Preferably, the sheet acts as the damp proof course of the building.

Preferably, the sheets of plastics material comprise sheets according tothe first aspect of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred embodiment of the present invention will now be described,by way of example only, with reference to the accompanying drawings, inwhich:

FIG. 1 is a schematic view and a magnified view of a sheet according topreferred embodiments of the present invention in a cavity barrierapplication;

FIG. 2 is a schematic view of the sheet of FIG. 1 in an alternativecavity barrier application including a separate damp proof course sheet;and

FIG. 3 is a schematic view of the sheet of FIG. 1 in a completeunderslab application.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

Referring to the figures, a sheet 10 for providing a barrier againstinsects according to preferred embodiments of the present invention isshown. The sheet 10 comprises a plastics material having an insecticidedispersed therethrough and retained in the plastics material. As willbecome apparent from the description below, the sheet 10 provides aphysical and chemical barrier to impede the penetration of insects byvirtue of the fact that it is manufactured from a plastics materialhaving an insecticide dispersed therethrough. The sheet 10 may alsoprovide a repellent barrier, ie. will repel insects away from itslocation if the plastics material also has a repellent dispersedtherethrough.

The sheet 10 has a vapour permeance of less than 0.02 mg/Ns andtherefore according to the Australian Standards is substantiallyimpermeable to water and can be used to form a moisture barrier for abuilding, for example.

The surfaces of the sheet 10 are substantially identical such that, whenthe sheet 10 is used, it may be laid with either surface facing up. Thesheet 10 is approximately 0.1-1 mm thick, preferably 0.2 or 0.5 mm thickwhen purposes of sheets 10 of these different thicknesses will bedescribed further on in the specification.

The plastics material may comprise any synthetic or semi-syntheticcompound formed by organic condensational polymerisation and which canbe moulded or extruded into objects or films or fibres. Such compoundsmay include, but are not limited to, polyamide (nylon), polyethylene,ethylene vinyl acetate, polystyrene, polyvinylchloride, synthetic rubber(eg. neoprene), polymethylmethacrylate (acrylic), polypropylene andpolyurethane. The plastics material may be formed from a combination oftwo or more of these compounds. The preferred compound used for theplastics material is low density polyethylene.

The plastics material may contain a UV stabiliser to prevent break downof the plastics material when exposed to sunlight. This is important inmaintaining the longevity of the sheet 10 which may be in use for up to50 or more years. The plastics material may also comprise a whitecolouring agent so that the sheet 10 is white in colour. The white sheet10 does not heat up as much as conventionally black plastic sheeting inthe sun and is therefore cooler and easier to handle duringinstallation.

The sheet 10 is substantially impact resistant, which guards againstrips or tears being formed in the sheet 10 during or after installation.The impact resistance of the sheet 10 is determined using the fallingdart impact test outlined in Australian Standard AS 4347.6. This testinvolves firstly, dropping a load of 310 grams from a drop height of 660mm, on the fold of the sheet 10. And secondly, dropping a load of 340grams and a drop height of 660 mm, the load is dropped twice per metrewidth of sheet 10 across the full width of the sheet 10 with the sheetpassing if 75% of these tests do not fail.

The insecticides which are retained in the plastics material may be anycompound that exhibits control or repellent affects against insectspecies, particularly termites. These compounds include, but are notlimited to, pyrethrum, synthetic pyrethroids, organo-chlorines,organo-sulfurs, carbamates, organo-phosphates, formamidines,nicotinoids, spinosyns, phenylpyrazoles, pyrroles, pyrazoles,dinitrophenols, pyridazinones, quinazolines, and benzoylureas.Preferably, a noted termiticide is used such as bifenthrin, permethrin,deltamethrin, lambda-cyhalothrin, cypermethrin, alpha-cypermethrin,zeta-cypermethrin, tetramethrin, and cyfluthrin. Some of theaforementioned insecticide compounds may also provide a repellenteffect, thereby creating the repellent barrier referred to above.

In a preferred embodiment, the insecticide is bifenthrin. Bifenthrin hasa non-alpha-cyano molecular structure which renders it a dermalnon-sensitiser, ie. does not react substantially with a person's skin.Thus, a person handling the sheet 10 is unlikely to experience anyreaction on their skin as a result of the bifenthrin in the plasticsmaterial.

Typically, the concentration of insecticide in the plastic is less than5 weight % and greater than 0.01 weight %. The concentration ofinsecticide is dependent upon the actual compound used. If theinsecticide is bifenthrin, as in the preferred embodiment discussedabove, then the concentration of the insecticide (bifenthrin) in theplastics material is 0.05 to 1.0 weight %, preferably 0.05 to 0.1 weight% and more preferably approximately 0.1 weight %.

Notably, bifenthrin provides a repellent barrier as well as a chemicalbarrier to the penetration of insects.

Manufacture of the sheet 10 involves mixing the insecticide with polymerresin to form a “mater batch”. The master batch has a higherconcentration of insecticide than the end sheet 10 product. Theconcentration of insecticide in the master batch may be as high as isstably supported in the polymer matric (ie. does not react and/or leachfrom the plastic).

For the sheet 10 of the preferred embodiment where the insecticide isbifenthrin, mixing the insecticide with polymer resin to form the masterbatch, in one embodiment involdes melting solid bifenthrin (>99%purity), melting the polymer resin separately (preferably low densitypolyethylene) and mixing the polymer resin and bifenthrin melts.Alternatively, powdered bifenthrin (mixed with talcum powder) or asolution of bifenthrin may be mixed with molten polymer resin to formthe master batch. In a preferred embodiment, the concentration ofbifenthrin in the master batch is approximately 2 weight %. However, theconcentration of bifenthrin in the master batch may be substantiallyhigher.

The master batch is solidified and formed into pellets, awaiting laterdilution to achieve the desired concentration of insecticide for the endsheet 10 product. Dilution of the master batch occurs by mixing thesolid master batch pellets with solid polymer pellets to form ahomogenous solid mixture. The homogenous solid mixture is melted andthen formed into the sheet 10 by any suitable means.

In one preferred embodiment, the sheet 10 is formed by blown film (ortubular film) extrusion of the molten monogenous mixture of plastic andinsecticide. Blown film extrusion involdes extruding the molten plasticthrough an annular slit die, usually vertically, to form a thin walledtube. Air is introduced via a hole in the centre of the die to blow upthe tube like a balloon. Mounted on top of the die, is a high-speed airring which blows onto the hot film to cool it. The tube of film thencontinues upwards, continually cooling, until it passes through niprolls where the tube is flattened to create what is known as a“lay-flat” tube of film. This lay-flat or collapsed tube is then takenback down the extrusion “tower” via more rollers. The lay-flat film isthen either kept as such or the edges of the lay-flat are slit off toproduce two flat film sheets 10 according to preferred embodiments ofthe present invention.

This blown film extrusion process is typically used to produce sheets 10approximately 0.2 mm thick. However, if thicker sheets 10 are requiredto be produced, particularly if the sheets 10 are approximately 0.5 mm,then an extrusion process is typically used. Referring in particular toFIGS. 1 and 2, the sheet 10 is shown in use in a cavity barrierapplication. FIGS. 1 and 2 show a building 11 having footings 20extending below the ground 12 and a concrete slab 21 which forms thebase of the building 11. The concrete slab 21 is integrally formed withthe footings 20. The footings 20 support the entire building 11.

Extending upwardly from the concrete slab 21 is an inner frame 23, whichis connected to the concrete slab 21 via a bottom plate 22. Extendingupwardly from the footings 20, approximately parallel to the inner frame23 is an outer wall 24. The outer wall 24 is spaced apart from the innerframe 23, such that a cavity 25 exists between them. As the cavity 25extends all the way around the building 11, should any termites gainaccess to the cavity 25 from the ground 12, then they may be able toattack a substantial portion of the building 11.

Thus, in FIGS. 1 and 2 the sheet 10 extends between the outer wall 24and the bottom plate 22 so as to block off access to the cavity 25 abovethe level of the concrete slab 21, creating a physical and chemicalbarrier against the penetration of insects. The physical barrier isprovided by the plastics material and the chemical barrier is providedby the insecticide dispersed through the plastics material from whichthe sheet 10 is manufactured. The insecticide does not significantlyleach from the plastic, but instead is retained so that theinsecticide's activity is expressed through the plastics material.Because the insecticide's activity is expressed within the plasticsmaterial it does not require a substrate such as soil to leach into inorder for the sheet 10 to work effectively. Thus, the sheet 10 is moreversatile and can be used in more varied applications than those of theprior art. If termites were to attack the sheet 10, then any contact oringestion of the insecticide containing plastics material will kill thetermites. This is because although the insecticide is tightly bound inthe plastics material and is not dislodged by water, there is stillenough insecticide available to deliver a lethal dose to an insect,which picks insecticide up upon contact with the sheet 10. Only a tinyamount of insecticide is required to kill the insect.

In FIG. 2, a further piece of sheeting 13 extends between the outer wall24 and the inner frame 23 on top of the sheet 10 and extends up theoutside of the inner frame 23. This further piece of sheeting 13 iscommonly referred to as “damp-proof course” and is primarily used as amoisture barrier to prevent moisture entering the cavity 25 above thesheet 10. As such, the damp-proof course 13 may simply be a plasticsheet, ie. contains no insecticide.

However, as shown in FIG. 1 (particularly in the magnified view), thesheet 10 may be employed as the damp proof course because in a preferredembodiment, the sheet 10 is impermeable to water and can therefore actas a moisture barrier. There is therefore no need for the additionalsheet 13 (as shown in FIG. 2) which saves time and cost in the buildingprocess. When installing the sheet 10 with the secondary purpose ofacting as the damp proof course, the sheet 10 should be doubled over atthe inner edge of the bottom plate 22 so that a portion of the sheet 10extends up the outside of the inner frame 23. The sheet 10 if used alsoas the damp proof course is approximately 0.5 mm thick. Otherwise, thesheet 10 (as shown in use in FIG. 2) may be only 0.2 mm thick.

Weepholes 26 are provided periodically along the length of the outerwall 24 to allow for moisture between the sheet 10 and the damp-proofcourse 13 to exit the building 11. An advantage of the present inventionis that because the insecticide is retained in the plastics material,that there will be extremely little or no insecticide leaking out of theweepholes 26 which could pose a human health risk.

The surfaces of the sheet 10 may be embossed so that there is frictionbetween the surface of the sheet 10 and any bricks laid above or belowthe sheet 10. This acts against any slippage occurring in the outer wall24 and/or the sheet 10. Alternatively, the sheet 10 may have at leastone smooth surface.

FIG. 3 shows the sheet 10 in a complete underslab application. The sheet10 is placed under the entire concrete slab 21, above the footings 20and across the cavity channel 25 to the outer wall 24. The sheet 10 mayalso extend at least partially up any penetrations 27 through theconcrete slab 21 such that it forms a tight fit with an elongate member(not shown) in the form of a conduit, pipe, cable, etc extending throughthe penetration 27. In this application, the sheet 10 acts as a barrieragainst entry by termites to the building through any part of theconcrete slab 21 and the cavity 25.

The sheet 10 could be used in a variety of other applications in abuilding 11, such as the perimeter of the concrete slab 21, lining theinside of the penetrations 27 and any other critical joints, retainingwalls and in any renovations or additions to the building 11. When thesheet 10 is used in a complete underslab application or in a retainingwall situation, the sheet 10 also acts as a moisture barrier.

EXAMPLES

The following examples further illustrate preferred embodiments of thepresent invention.

Example 1 Efficacy Test of a Polymer Sheet Containing Bifenthrin forSubterranean Termite Control

A replicated field trial conducted in the Northern Territory ofAustralia evaluated a plastic sheet product containing bifenthrinaccording to preferred embodiments of the present invention, as abarrier against field colonies of the Australian subterranean termitescomprising Mastotermes drawiniensis and the mound building form ofCoptoteres acinaciformis. A range of bifenthrin concentrations was usedin the assessment including untreated plastic sheet, and a sheetcontaining 0.1% bifenthrin. Each test was replicated ten times for eachof the termite species giving a total number of replicates of twenty.

TABLE 1 Summary of residual protection performances of bifenthrincontaining sheet as a barrier against termites after 2 years assessment.Mastotermes Coptotermes Combined total all darwiniensis acinacifoimisspecies 0.1% 0.1% 0.1% 0% bifenthrin Control bifenthrin Controlbifenthrin Number of 7 0 (10) 9 (10) 0 (10) 16 (20) 0 (20) pene- (10)trations out of possible (10) % of 70% 0% 90% 0% 80% 0% replicatesbreeched by termites

The results indicate that in the tropical north, under extreme pressurefrom the two most economically important and destructive termite species(Mastotermes darwiniensis, and Coptotexmes acinaciformis) in Australia,the sheet containing 0.1% bifenthrin is capable of providing 100%protection from concealed entry through the sheet. Whilst these twospecies were targeted Heterotexmes sp., Microcerotermes sp., andSchedorhinotermes sp. also contacted the sheets.

In assessing the trial, it was noted that termites were exhibitingclassical symptoms of repellence from the bifenthrin containing sheet.Symptoms included reduced faecal plastering on the bifenthrin containingsheet, and veneering of attractant wood directly in contact with thebifenthrin containing sheet. It was also noted that there were deadtermites present on the sheet containing 0.1% bifenthrin.

Example 2 Potential for Degradation of Bifenthrin in a Polymer Sheet

Trials were conducted to investigate the degradation of bifenthrin in asheet according to preferred embodiments of the present invention undera range of simulated installations including full under slab andperimeter cavity situations. Sheet material containing threeconcentrations of bifenthrin was assessed for degradation (0.05% and0.1%).

Samples of the sheeting were taken at 0, 1, 3, 6, and 12 months afterapplication for under-slab simulated installations and at 0, 3, and 6months after application for perimeter cavity simulated installations.The under slab simulated conditions also investigated influence of soiltype by including a clay soil and a sandy soil in contact with the sheetproduct.

The results from these trials indicate that there has been no change (atthe 95% confidence level) in the amount of bifenthrin present in thesheet over the period of the trial. There has been no significantbreakdown or migration of the active ingredient out of the sheet.

TABLE 2 Statistical analysis results (as determined by one-way ANOVA) ofdata generated for bifenthrin sheet in contact with sand and clay soilsin an under-slab simulation, and in a perimeter cavity situation. Timeperiod Statistical for difference in Test Nominal comparisonconcentration situation Soil Type concentration (months) over timeUnder-slab Clay 0.05%  0-12 not significant (P > 0.05) Under-slab Sand0.05%  0-12 Not significant (P > 0.05) Under-slab Clay 0.1% 0-12 Notsignificant (P > 0.05) Under-slab Sand 0.1% 0-12 Not significant (P >0.05) Perimeter NA 0.05%  0-6  Not cavity significant (P > 0.05)Perimeter NA 0.1% 0-6  Not cavity significant (P > 0.05)

Example 3 Potential for Leaching of Bifenthrin from a Sheet Matrix

A study was conducted to evaluate the potential for bifenthrin containedin a plastic sheet according to preferred embodiments of the presentinvention to migrate into water.

In the trial a sample of a plastic sheet containing 0.1% bifenthrin wasplaced in water, and gently stirred once a week, for a period of sixmonths. The plastic sheet and the water were analysed to determine theamount of bifenthrin that had moved into the water at 0, 1 and 6 months.

The analysis of variance showed that there was no significant loss(P>0.05) of bifenthrin from the sheeting product and no significantincrease (P>0.05) of bifenthrin in the water after six months comparedto the time zero levels.

TABLE 3 One-way alaysis of variance of bifenthrin concentration in theWater Water (μg/mL) F-test P value Significance Time 0 v 1 month 0.4660.736 No significant difference (P > 0.05) Time 0 v 6 months 0.379 0.782No significant difference (P > 0.05)

TABLE 4 One-way analysis of variance of bifenthrin concentration in thePlastic Plastic (μg/g) F-test P value Significance Time 0 v 1 month20.783 0.017 No significant difference (P0.05) Time 0 v 6 months 2.0100.279 No significant difference (P > 0.05)

In the preceding description of the invention, except where the contextrequires otherwise due to express language or necessary implication, theword “comprise” or variations such as “comprises” or “comprising” isused in an inclusive sense, ie. to specify the presence of the statedfeatures but not to preclude the presence or addition of furtherfeatures in various embodiments of the invention.

1. A sheet for providing a barrier against the penetration of insects,the sheet comprising at least one insecticide distributed through aplastics material wherein the insecticide is substantially retained inthe plastics material.
 2. A sheet as claimed in claim 1, wherein thesheet is approximately 0.1-1 mm thick.
 3. A sheet as claimed in eitherclaim 1 or 2, wherein the plastics material is any synthetic orsemi-synthetic compound formed by organic condensational polymerisation.4. A sheet as claimed in either claim 1 or 2, wherein, the plasticsmaterial is any one or a combination of polyamide (nylon), polyethylene,polyvinylchloride, ethyl vinyl acetate, polystyrene, synthetic rubber(eg. neoprene), polymethylmethacrylate (acrylic), polypropylene andpolyurethane.
 5. A sheet as claimed in either claim 1 or 2, wherein, theplastics material is low density polyethylene.
 6. A sheet as claimed inany of the preceding claims, wherein the plastics material contains a UVstabiliser.
 7. A sheet as claimed in any one of the preceding claims,wherein the plastics material contains a white colouring agent.
 8. Asheet as claimed in any one of the preceding claims, wherein the sheetis substantially impermeable to water.
 9. A sheet as claimed in any ofone of the preceding claims, wherein the at least one insecticide is anycompound that exhibits sufficient lethal control and/or repellenteffects against insects.
 10. A sheet as claimed in any one of claims 1to 8, wherein the at least one insecticide is any one or combination ofpyrethrum, synthetic pyrethroids, organo-chlorines, organo-sulfurs,carbamates, organo-phosphates, formamidines, nicotinoids, spinosyns,phenylpyrazoles, pyrroles, pyrazoles, dinitrophenols, pyridazinones,quinazolines, and benzoylureas.
 11. A sheet as claimed in any one ofclaims 1 to 8, wherein the insecticide is bifenthrin.
 12. A sheet asclaimed in claim 11, wherein the concentration of bifenthrin in theplastic is 0.05 to 1.0 weight %.
 13. A sheet as claimed in claim 11,wherein the concentration of bifentrin in the plastic is approximately0.1 weight %.
 14. A method of protecting a building against thepenetration of insects into the building, the method comprising the stepof positioning one or more sheets of a plastics material above thefootings of the building, wherein the plastics material contains atleast one insecticide distributed therethrough.
 15. A method as claimedin claim 14, wherein the step of positioning the sheets of plasticsmaterial further involves positioning the sheets around the perimeter ofthe building at least extending between an outer wall of the buildingand an inner frame of the building.
 16. A method as claimed in eitherclaim 14 or 15, wherein the sheets of plastics material comprise sheetsas claimed in any one of claims 1 to
 13. 17. A sheet for providing abarrier against the penetration of insects, the sheet enabled to bepositioned around the perimeter of a building at least extending betweenan outer wall of the building and an inner frame of the building, thesheet comprising at least one wherein the insecticide is substantiallyretained in the plastics material.